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After a case of mistaken identity and a short stint in a small dolphinarium called Marineland, Billie the bottlenose dolphin was released back into the wild in 1988. Before her capture, Billie was locally famous for her antics in Port River, an estuary that curves along the ports of Adelaide, Australia. A racehorse trainer would send his horses into the river as a form of exercise and Billie liked to swim around them. Once she was back in Port River, Bille began to exhibit a different type of delightful behavior: tail walking.

Tail walking, scientists explain in a study released this month, is not something that bottlenose dolphins do naturally. It doesn’t seem to have any adaptive function. When a wild dolphin juts its body out of the water vertically, vigorously pumping its tail to stay above the surface like some oceanic, moonwalking Michael Jackson, there are no obvious benefits. Yet, citizens and scientists saw Billie tail walking on a total of 279 occasions until her death in 2009. First author and scientist Mike Bossley, Ph.D., says much of these tail flips were serendipitously documented while researchers worked on other dolphin studies.

“Although the behavior has no obvious adaptive function, I don’t think it was only play — although, that is likely part of it,” study co-author and University of St. Andrews biology reader Luke Rendell, Ph.D., tells Inverse. “I think this report speaks to the importance of the social function of imitation in this species.”

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The tail-walking dolphins live in Port River.
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Billie wasn’t the only tail-walking dolphin in the river. In 2006, almost two decades after Billie was released from the dolphinarium, another dolphin called Wave began to tail walk as well. Wave’s tail walking increased rapidly after Billie died and, subsequently, several other dolphins in her community were seen tail walking, too. Between 2009 and 2014, 76 percent of the tail walks were seen in the presence of other dolphins — and all of the dolphins that tail walked were female.

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Wave tail walks.

Billie’s own tail walking is thought to have emerged as imitation. At Marineland, she was housed with five other dolphins, all of which were trained to perform tricks like tail walking in public shows. Billie was never trained, but she could observe the captive dolphins as they practiced the stunt.

That these dolphins are imitating each other, says Rendell, is what intrigues him most about this whole situation.

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“While this role [imitation] has been well-understood as a critical part of human development for some time, in non-humans, study of imitation has focused on adaptive behaviors like foraging and migration,” Rendell explains.

When human children and infants imitate, they are believed to be engaging in cultural transmission. Our developmental pathway is paved with behavioral imitation because copying becomes a means of transmitting social information. Babies imitate behavior before they know whether or not that behavior is going to help them down the line. The important thing is that they try.

Eventually, something works and that behavior is passed down through generations, a process that results in it becoming a cultural tradition. Imitation is a well-established practice among all animals, but the difference between orcas learning to hunt together and dolphins tail walking is that the former has an obvious biological function — eating — while the other does not. That’s where the bottlenose dolphin mystery lies.

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Rendell reasons there could be multiple interpretations of the dolphins’ tail walking. It could be a dominance thing. Billie died and Wave became the new tail-walking queen. It could be an alliance strategy. Just like male dolphins synchronize and work together, this could be the first hint of female teamwork. Perhaps the tail walking that persists today is an attempt to process Billie’s death by the pod and strengthen their social bond. Or maybe tail walking is like the signature whistles dolphins use to identify each other — a physical identifying signature.

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A Port River dolphin tail walks.

“However, all of these are grossly speculative,” says Rendell. “There is so much we don’t know about the social lives and minds of these animals. Anyone who tells you they ‘know’ is spinning a line, and we must be wary of naively projecting our human experiences onto them.”

What one can take away from this, he argues, is that imitation plays a clearly important social role in dolphin societies much like it does in our own. The parallels between the two are increasing in number, just like the tail walks over in Port River.